1. Field of the Invention
The present invention pertains to a well pumping unit for operating a downhole, rod actuated oil well pump and the like. The well pumping unit includes a control system which includes means for sensing the lifting effort on the pump rod, controlling an operating cycle of the pumping unit and for varying the effective weight of a counterweight system.
2. Background
Various types of well pumping units for operating downhole positive displacement well pumps, also known as sucker rod pumps, have been developed. The most common type of well pumping unit comprises a walking beam mechanism which reciprocates the elongated pump rod or sucker rod string and is driven by an electric motor or internal combustion engine through a gear reduction mechanism including, in some cases, a counterweight system. There are several desiderata which have not been met by prior art pumping systems. For example, it is desirable to provide a well pumping unit which is easily set up at the well site and is easily connected to and disconnected from the elongated pump rod string so that servicing of the pumping unit itself or workover of the well may be easily performed. It is also desirable to minimize the stresses on the elongated pump rod string to reduce the change of pump rod or downhole pump failure.
In particular, the pumping of low productivity oil wells, sometimes referred to as stripper wells, requires a pumping unit which is economical to operate and can be controlled to avoid overpumping the well. Many oil bearing formations produce gases, water and other fluids which are mixed in with the produced crude oil. These fluids affect the lifting requirements of the pumping unit and the rate of flow of fluids in the wellbore is often erratic and inconsistent, particularly informations which are being subjected to enhanced recovery operations or are nearing the end of their productive life.
All of the above mentioned requirements and desired features in well pumping units have not been met by prior art type pumping units and control systems therefor. It is to this end that the present invention has been developed with a view to providing an improved well pumping unit and control system which is reliable in operation, economical to manufacture, and easily adapted to operate efficiently for lifting crude oil and other well fluids from formations which have erratic production characteristics or are marginally productive.